Water-based fluids, such as metal working fluids, hydraulic fluids and coolants, undergo after some time of use or storage undesirable changes which can be related to the fact that the components included in the fluids are degraded by bacteria, fungi and other microorganisms. The microbial degradation considerably reduces the life and the performance of the fluids. From an economic point of view, it is therefore of great importance that microbial degradation of fluids of this type be minimized.